Using detailed linguistic analysis, this study examined the expository writing abilities of school-age children with autism spectrum disorder (ASD) in comparison to neurotypical (NT) children. Associations between executive functioning (EF) and writing ability in children with and without ASD were also explored. Compared to NT peers, children with ASD wrote shorter expository texts that contained more grammatical errors, and needed more assistance from the experimenter to complete the writing assessment. However, the texts of children with and without ASD did not differ in their lexical diversity, use of writing conventions, and overall quality. Analyses also revealed that greater EF was associated with better writing outcomes in both groups. Educational implications of these findings are discussed.